1. Field of the Invention
The present invention relates to an image capturing apparatus and control method therefor which can switch between an optical viewfinder and live view.
2. Description of the Related Art
A large number of cameras equipped with an electronic viewfinder (hereinafter referred to as a live view) as well as with a conventional optical viewfinder have been proposed, where the electronic viewfinder displays images captured using an image sensor on a liquid crystal monitor or the like. The live view features tolerance for a dark environment, that is, low luminance; ease of checking for depth of field; and ease of display manipulation such as enlargement.
A single-lens reflex camera performs auto focus control (AF) using a phase difference detection method which involves separating light that has passed through an imaging lens with a separator lens, achieves focus by determining a lens displacement amount based on distances between images formed by respective beams of separated light. On the other hand, for a camera equipped with a live view function, the dominant method is a contrast method that achieves focus based on contrast of image data obtained by an image sensor.
To make full use of the features of the optical viewfinder and live view mode, a technique has been proposed which allows even a single-lens reflex camera to be used by switching between the two methods (see, for example, Japanese Patent Laid-Open No. 5-107595). When the camera is switchable between the optical viewfinder and live view mode, the AF methods work in each mode as follows. That is, AF based on the phase difference detection method (hereinafter referred to as “phase difference AF”) is used with the optical viewfinder and AF based on the contrast method (hereinafter referred to as “contrast AF”) is used in the live view mode. Each AF method has its features: specifically, for example, the phase difference AF provides high focusing speed while the contrast AF provides high focusing accuracy. Therefore, the user may want to perform phase difference AF when using live view, and a camera capable of switching between AF methods have also been proposed (see, for example, Japanese Patent Laid-Open No. 2001-272593).
An image capturing apparatus has also been proposed which allows electronic zooming and trim display by taking advantage of the features of live view. In this connection, it is proposed to retain a focus detection area with respect to a subject when an electronic zoom magnification is changed (see, for example, Japanese Patent Laid-Open No. 2002-209134) or to zoom around a subject area (see, for example, Japanese Patent Laid-Open No. 2005-033508).
When phase difference AF is performed in conjunction with contrast AF during the use of live view, it is conceivable to allow the user to separately set the focus detection area used for contrast AF and focus detection area used for phase difference AF. In this case, use of electronic zooming or trim display may cause the focus detection area of the phase difference AF selected by the user to move out of an angle of view of live view. Techniques described in Japanese Patent Laid-Open Nos. 5-107595, 2001-272593, 2002-209134, and 2005-033508 do not give particular consideration to these conditions. This presents a problem of poor usability, such as the need for a user to select the focus detection area of the phase difference AF anew.